The present invention relates to a technique for transmitting/receiving signals from/in a wireless LAN system, more particularly to a technique to be employed effectively for auto gain controlling of received signals.
A wireless LAN (Local Area Network) usually needs auto gain controlling for correcting the signal level of each received signal according to the signal strength.
The IEEE802.11a standard makes arrangements for such auto gain controlling, as well as synchronization detecting, etc. to be carried out at the initial part of each received packet signal, that is, in the 8 μs preamble period of the signal, so that the gain controlling must be completed actually within a period of 5 μs or so.
In the examination carried out by the present inventors, two semiconductor integrated circuit devices are used for RF (high frequency) processing and baseband processing in such auto gain controlling.
The semiconductor integrated circuit device for RF processing converts received signals to baseband signals. The semiconductor integrated circuit device for baseband processing converts signals whose frequencies have been changed by an RF chip to digital signals, then measures the level of each of the digital signals to control the signal level.
While the semiconductor integrated circuit device for RF processing receives signals within a level range of −82 dBm to −30 dBm, the semiconductor integrated circuit device for baseband processing must control signal levels within a range of ±2 dBm. If the semiconductor integrated circuit device for baseband processing receives a weaker level digital signal, the circuit device comes to perform an auto correlation processing for the signal and uses the signal for controlling the signal level.
Such a wireless LAN system is described in detail in the “Standard LAN Guidebook” (the second volume)(revised third edition), pp235 to 238, edited by Multimedia Communication Kenkyu-kai, published by Askii Inc., Aug. 1, 1998). This guidebook describes a wireless LAN architecture conforming to the IEEE802.11.